Instant messages are short text messages with no subject and no attachments sent directly from terminal to terminal within an instant messaging (IM) community. The messages are generally displayed to the user as part of a conversation. A member of an instant messaging (IM) community has a unique identifier (“contact name”) in that community and can be added to the contact list of another member of the community using that identifier. For example, SMS is available only within the community of mobile telephone users, and the unique identifier is the telephone number.
Some IM systems include presence information about the availability of one's contacts for communication. Presence information is particularly important when a contact uses a wireless-enabled mobile device, because the contact may become unavailable with short notice due to battery loss, poor network coverage, and the like. Moreover, for wireless-enabled mobile devices that are always connected, the contact may appear to be available even if he or she is not.
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